* Put both hidden categories and normal categories into the view page HTML, but with hidden categories being unconditionally hidden with CSS. A JS show/hide toggle can be added in user/site JS.
* Add user preference to always show hidden categories
* Add all hidden categories to [[Category:Hidden categories]], localised by hidden-category-category
* Add wgVariantArticlePath and wgActionPaths to the JS variables script, needed to determine title from link href.